1. Field of the Invention
The present invention relates to a method for manufacturing a lens, an apparatus for manufacturing a lens, and a method for manufacturing an optical apparatus.
2. Description of the Related Art
In a zoom lens of a camera, in order to correct a chromatic aberration, a plurality of lenses is used. On the other hand, when a radial gradient index lens having a refractive index distribution in a radial direction from an optical axis is used, even if the number of lenses is small, the chromatic aberration can be corrected. Therefore, when a radial gradient index lens is used, the reduction in size of a zoom lens can be realized.
A radial gradient index lens can be manufactured, for example, by forming a composition distribution from at least two types of monomers having different refractive indices. In particular, a concave or a convex plastic lens is obtained by the steps of heating a monomer injected in a casting mold to form a gel, holding another monomer in contact with the periphery of the gel for a predetermined time for diffusion, and subsequently heating the entire composite thus formed for curing (Japanese Patent Laid-Open No. 7-40357, hereinafter referred to as “Patent Document 1”). That is, the distribution of the refractive index is to be adjusted by changing the time for diffusion. In addition, a method of manufacturing a gradient index lens material has been disclosed in which polymerizable molecules are diffused in a cylindrical material composed of prepolymers with refractive index higher than that of the polymerizable molecules (Japanese Patent Laid-Open No. 58-98316, hereinafter referred to as “Patent Document 2”). In addition, in Patent Document 2, a laser beam is made incident at a position on one flat surface of the cylindrical material with an angle, a laser beam receiving device is provided so as to detect an position and an angle of a outgoing beam which outgoes from the other flat surface of the cylindrical material when the gradient in the concentration of the polymerizable molecules forms a predetermined refractive index distribution, and the diffusion of the polymerizable molecules is stopped when the outgoing beam is detected.
By the steps described above, a gradient index lens material can be manufactured with good reproducibility.
However, in the manufacturing method disclosed in Patent Document 1, when the diffusion rate of the another monomer is changed, for example, by a sudden change in temperature in a diffusion step, or when manufacturing is performed under conditions in which temperature control is difficult to perform, a lens having a desired refractive index distribution may not be obtained in some cases. In addition, in Patent Document 2, since thin light beams such as laser beams are used, it may not be detected that a desired refractive index distribution is not formed over the entire lens in some cases such that a refractive index distribution is formed in a certain portion but is not formed in the other portion.